The present invention relates to an improved insulating sheet material and to cigarettes and other smoking articles which employ the insulating sheet material as one or more components thereof. The improved insulating material is particularly useful in smoking articles having a fuel element and a physically separate aerosol generating means, e.g. as an insulating member for insulating the fuel element. In general, the sheet material of the present invention is formable without the use of any organic binder and comprises an inorganic fibrous material such as calcium sulfate, calcium sodium phosphate, or mixtures thereof, and a relatively small amount of highly refined fibrillated cellulose-based fibers such as wood pulp.
Cigarettes, cigars and pipes are popular forms of tobacco smoking articles. Many smoking products and smoking articles have been proposed through the years as improvements upon, or as alternatives to, these popular forms of tobacco smoking articles, particularly cigarettes.
Many, for example, have proposed tobacco substitute smoking materials. See, e.g., U.S. Pat. No. 4,079,742 to Rainer et al. Two such materials, Cytrel and NSM, were introduced in Europe in the 1970's as partial tobacco replacements, but did not realize any long-term commercial success.
Many others gave proposed smoking articles, especially cigarette smoking articles, based on the generation of an aerosol or a vapor. See, for example, the background art cited in U.S. Pat. No. 4,714,082 to Banerjee et al.
Recently, in European Patent Publication Nos. 0174645 and 0212234, U.S. Pat. No. 4,714,082 to Banerjee et al. and U.S. Pat. No. 4,756,318 to Shannon et al., assigned to R. J. Reynolds Tobacco Co., there are described smoking articles, especially cigarette smoking articles, which are capable of providing the user with the pleasures associated with smoking, by heating but not burning tobacco and without delivering appreciable quantities of incomplete combustion or pyrolysis products. The improved insulating sheet material of the present invention is particularly suited for use with such articles.
Calcium sulfate, also commonly referred to as gypsum, has been used by artists and builders for thousands of years.
Recently, calcium sulfate has been produced in a fibrous form, primarily as a filler for reinforcement in thermoset and thermoplastic systems, such as polyesters, urethanes, epoxies, silicones, polypropylene, nylon, etc. In these systems calcium sulfate is used as a partial replacement for glass fibers and other reinforcing materials.
Another inorganic filler is calcium sodium phosphate. Like calcium sulfate, it too has been widely used in a variety of materials, primarily as a filler, such as for composites in organic polymeric materials. U.S. Pat. No. 4,346,028 to Griffith et al. discloses very thin, flexible calcium sodium phosphate fibers which are insoluble in water, and which are acid, alkali and temperature resistant. Described uses for such crystals/fibers include mats and felts, as reinforcing agents for cellulosic papers and fibers, as a substitute for asbestos in asbestos/cement mixtures, as an additive to oil-based and latex paints to change the drying properties of the paint, and to form laminates and composites with organic polymeric materials.
In U.S. Pat. No. 4,609,433 to Crutchfield et al., there is described the use of crystalline calcium M phosphate fibers as a replacement or substitute for asbestos in the manufacture of fibrous sheets. The sheet comprises the crystalline calcium M phosphate fibers (65-95% by weight), auxillary fibers such as wood pulp or synthetic fibers (1-15% by weight) having a Canadian freeness from about 300 ml to about 700 ml, and a water insoluble organic polymeric binder (5-30% by weight).
Japanese Patent Application Kokai No. 61-101438 describes a method of manufacturing gypsum paper with 50-96 parts by weight calcium sulfate, 2-20 parts by weight pulp, 2-30 parts by weight fibrous material, and 0.5-5 parts by weight fixing agent.